This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the subject matter described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, not as admissions of prior art.
The present disclosure relates generally to making measurements of subsurface formations surrounding a wellbore using one or more downhole tools of a bottom hole assembly (BHA) that is integral to a drill string and, more particularly, to the electrical power and communication buses between the downhole tools making up the BHA.
Logging tools have long been used in wellbores to make, for example, formation evaluation measurements to infer properties of the subsurface formations surrounding the borehole and the fluids in such formations. Examples of common logging tools include electromagnetic tools, nuclear tools, and nuclear magnetic resonance (NMR) tools. Aside from these examples, various other tool types may also be used for evaluation of subsurface formation properties, such as acoustic logging tools.
Early logging tools were typically run into a wellbore using a wireline cable after the wellbore had been drilled. Modern versions of such wireline tools are still used extensively today. However, the desire for information while drilling the borehole gave rise to the development of measurement-while-drilling (MWD) tools and logging-while-drilling (LWD) tools. MWD tools typically provide drilling parameter information, such as weight on the bit, torque, temperature, pressure, direction, and inclination. LWD tools typically provide formation evaluation measurements such as resistivity, porosity, and NMR distributions (e.g., T1 and T2 relaxation times). MWD and LWD tools often have components common to wireline tools (e.g., transmitting and receiving antennas). However, MWD and LWD tools are also designed and constructed to endure the harsh environment of drilling.
A BHA typically includes a single MWD tool and several LWD tools that are connected by a low power tool bus (referred to as “LTB” or “LTB bus”). The LTB bus provides power to the logging tools and also provides a communication link by which the tools can communicate with one another. For example, the source of this power can be a turbine generator in the MWD tool that is driven by pressurized drilling fluid (“mud”) when mud pumps are on. However, the turbine generator of an MWD has limitations on the amount of power it can provide, thus restricting the possible configurations of a BHA, or at the very least limiting the number of tools in a BHA that can be operated simultaneously. As the industry continues to explore and drill to greater depths (e.g., depths of 20,000 feet or more) in the search of producible subsurface hydrocarbon formations, BHAs have continued to increase in complexity such that existing MWD modules may have difficulty supplying sufficient power for an entire BHA.